/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.editor.VariableRemapper;
import proguard.classfile.util.*;
import proguard.classfile.visitor.*;
import proguard.optimize.info.*;

/**
 * This AttributeVisitor removes unused parameters from the code of the methods that it visits.
 *
 * @see ParameterUsageMarker
 * @see MethodStaticizer
 * @see MethodDescriptorShrinker
 * @author Eric Lafortune
 */
public class ParameterShrinker extends SimplifiedVisitor implements AttributeVisitor {
    // *
    private static final boolean DEBUG = false;
    /*/
    private static       boolean DEBUG = System.getProperty("ps") != null;
    //*/

    private final MemberVisitor extraUnusedParameterMethodVisitor;

    private final VariableRemapper variableRemapper = new VariableRemapper();

    /**
     * Creates a new ParameterShrinker.
     */
    public ParameterShrinker() {
        this(null);
    }

    /**
     * Creates a new ParameterShrinker with an extra visitor.
     * 
     * @param extraUnusedParameterMethodVisitor an optional extra visitor for all removed parameters.
     */
    public ParameterShrinker(MemberVisitor extraUnusedParameterMethodVisitor) {
        this.extraUnusedParameterMethodVisitor = extraUnusedParameterMethodVisitor;
    }

    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        // Get the original parameter size that was saved.
        int oldParameterSize = ParameterUsageMarker.getParameterSize(method);

        // Compute the new parameter size from the shrunk descriptor.
        int newParameterSize =
            ClassUtil.internalMethodParameterSize(method.getDescriptor(clazz), method.getAccessFlags());

        if (oldParameterSize > newParameterSize) {
            // Get the total size of the local variable frame.
            int maxLocals = codeAttribute.u2maxLocals;

            if (DEBUG) {
                System.out.println("ParameterShrinker: " + clazz.getName() + "." + method.getName(clazz)
                    + method.getDescriptor(clazz));
                System.out.println("  Old parameter size = " + oldParameterSize);
                System.out.println("  New parameter size = " + newParameterSize);
                System.out.println("  Max locals         = " + maxLocals);
            }

            // Create a variable map.
            int[] variableMap = new int[maxLocals];

            // Move unused parameters right after the parameter block.
            int usedParameterIndex = 0;
            int unusedParameterIndex = newParameterSize;
            for (int parameterIndex = 0; parameterIndex < oldParameterSize; parameterIndex++) {
                // Is the variable required as a parameter?
                if (ParameterUsageMarker.isParameterUsed(method, parameterIndex)) {
                    // Keep the variable as a parameter.
                    variableMap[parameterIndex] = usedParameterIndex++;
                } else {
                    if (DEBUG) {
                        System.out.println("  Deleting parameter #" + parameterIndex);
                    }

                    // Shift the variable to the unused parameter block,
                    // in case it is still used as a variable.
                    variableMap[parameterIndex] = unusedParameterIndex++;

                    // Visit the method, if required.
                    if (extraUnusedParameterMethodVisitor != null) {
                        method.accept(clazz, extraUnusedParameterMethodVisitor);
                    }
                }
            }

            // Fill out the remainder of the map.
            for (int variableIndex = oldParameterSize; variableIndex < maxLocals; variableIndex++) {
                variableMap[variableIndex] = variableIndex;
            }

            // Set the map.
            variableRemapper.setVariableMap(variableMap);

            // Remap the variables.
            variableRemapper.visitCodeAttribute(clazz, method, codeAttribute);
        }
    }
}
